The present disclosure relates to a controllable optical attenuator. More particularly, the disclosure relates to a controllable optical attenuator with which the attenuation of an optical signal can be quickly adjusted with minimal power consumption.
Lasers are used in the communications field to transmit optical signals through communications networks. Although it is generally preferable that high power signals are transmitted to ensure accurate transmissions over long distances, it is often necessary to attenuate these signals to reduce their intensity. For instance, attenuation may be necessary to prevent saturation of nearby receivers. In addition, attenuation is often necessary when testing the dynamic range of a receiver.
Signal attenuation normally is provided by optical attenuators. Conventional attenuators typically comprise mechanical filter elements that are moved in and out of the transmission path. One common mechanical filter is the disk filter. Disk filters typically include a plurality of absorption filter elements arranged at various predetermined angular positions about the periphery of the disk. The various absorption filters of the disk can be independently placed within the transmission path under the driving force of a motor.
Although disk filters do provide attenuation of transmitted signals, their use presents several disadvantages. First, disk filters have relatively slow response times due to the time required for the filter mechanism to rotate the disk to the correct angular position. In addition, use of conventional disk filters normally results in high insertion losses due to the coupling losses associated with insertion of the filters between two waveguides. Because disk filters usually require a motor to drive the disk, disk filter mechanisms also tend to be bulky and are therefore ill-suited for portable applications. Moreover, because such mechanisms comprise several moving parts, regular maintenance normally is required for these mechanisms.
Non-mechanical attenuator designs have been created in an effort to avoid the aforementioned drawbacks of mechanical filters. In some designs, liquid crystal (LC) filters provide the desired attenuation. Although LC filters do not have many of the problems associated with conventional mechanical filters, LC filters present other disadvantages. For instance, LC filters are not bistable and therefore require power both in the switching and the holding states. In addition, LC filters are sensitive to temperature change. More particularly, the refractive index of LC filters can change in response to changes in ambient temperature. For this reason, LC filters can be difficult to control. Additionally, current designs of LC filters tend to have relatively small dynamic ranges and often have difficulties with backscattering.
From the foregoing, it can be appreciated that it would be desirable to have a controllable optical attenuator that responds quickly, consumes little power, has low insertion loss, and that has no moving parts.
The present disclosure relates to a controllable optical attenuator. The attenuator generally comprises an optical waveguide that extends longitudinally along the optical attenuator. The optical waveguide has an exposed surface and a core that is positioned directly adjacent the exposed surface. The attenuator further comprises at least one elongate chamber that is formed transversely to the longitudinal extent of the optical waveguide, with the exposed surface of the optical waveguide forming part of the chamber. In addition, the attenuator includes a liquid droplet that is disposed within the elongate chamber, the droplet being movable along the chamber from a position lateral of the optical waveguide exposed surface to a position in which contact is made between the liquid droplet and the optical waveguide exposed surface. When the liquid droplet is positioned so as to contact the exposed surface of the optical waveguide, a portion of the optical signal transmitted along the waveguide core is absorbed by the droplet so as to attenuate the transmitted signal.
In addition, the present disclosure relates to a method of attenuating a transmitted optical signal. The method comprises providing an optical transmission path along an optical waveguide, forming an elongate chamber transverse to the optical transmission path, providing a liquid droplet within the elongate chamber, and moving the liquid droplet along the elongate chamber from a position lateral of the optical transmission path to a position directly adjacent the optical transmission path such that a portion of the transmitted optical signal is absorbed by the liquid droplet.
The features and advantages of the invention will become apparent upon reading the following specification, when taken in conjunction with the accompanying drawings.